Kepler-432 b: a massive warm Jupiter in a 52-day eccentric orbit transiting a giant star

TL;DR

This paper confirms Kepler-432 b as a massive warm Jupiter orbiting a giant star with high eccentricity, providing insights into planetary evolution around evolved stars and suggesting potential additional companions.

Contribution

It presents the first confirmed transiting warm Jupiter around a giant star, with precise radial velocity measurements and analysis of its orbital characteristics.

Findings

Kepler-432 b has a mass of approximately 5.84 Mjup.

It orbits its star every 52 days with an eccentricity of 0.478.

Evidence suggests a possible third object in the system.

Abstract

We study the Kepler object Kepler-432, an evolved star ascending the red giant branch. By deriving precise radial velocities from multi-epoch high-resolution spectra of Kepler-432 taken with the CAFE spectrograph at the 2.2m telescope of Calar Alto Observatory and the FIES spectrograph at the Nordic Optical Telescope of Roque de Los Muchachos Observatory, we confirm the planetary nature of the object Kepler-432 b, which has a transit period of 52 days. We find a planetary mass of Mp=5.84 +\- 0.05 Mjup and a high eccentricity of e=0.478 +\- 0.004. With a semi-major axis of a=0.303 +\- 0.007 AU, Kepler-432 b is the first bona fide warm Jupiter detected to transit a giant star. We also find a radial velocity linear trend of 0.44 +\- 0.04 m s$^{-1}$ d$^{-1}$, which suggests the presence of a third object in the system. Current models of planetary evolution in the post-main-sequence phase predict that Kepler-432 b will be most likely engulfed by its host star before the latter reaches the tip of the red giant branch.